1. FIELD OF THE INVENTION
The invention relates to a method and a circuit arrangement for converting an analog measuring voltage into a digital measurement signal and is based on the fact that in accordance with the state of the art the measuring voltage on the one hand and reference voltages on the other hand are supplied to the inputs of a plurality of comparators and the measurement signal is read off at the outputs of the comparators.
2. THE PRIOR ART
If, in accordance with the state of the art, it is intended to convert a measuring voltage into, for example, a digital measuring voltage with eight discrete measured values, eight comparators are required; thus one comparator is required for each discrete measured value. This is relatively complicated, so that it is an object of the invention to recite a less complicated method or a less complicated circuit arrangement for converting an analog measuring voltage into a digital measurement signal.
The method in accordance with the invention by means of which the above identified object is attained, is firstly and essentially characterized in that the reference voltage from the second comparator is dependent on the output signal of the first comparator, that the reference voltage for the third comparator is dependent on the output signal of the first comparator and/or the output signal of the second comparator, etc., and in that the total of all output signals of all comparators represents the measurement signal in a coded form. Accordingly, the circuit arrangement in accordance with the invention is firstly and essentially characterized in that the reference voltage for the second comparator is controllable with the aid of the output signal of the first comparator, the reference voltage for the third comparator is controllable with the aid of the output signal of the first comparator and/or the output signal of the second comparator, etc., and in that the measurement signal can be represented with the aid of the total of all the output signals of all the comparators.
In accordance with the state of the art, eight comparators are required if a measuring voltage in the range of, for example, 0 V to 8 V is to be converted into a digital measurement signal in such a way that eight discrete measured values can be represented; the output of the first comparator represents the value 0-1 V, the output of the second comparator the value 1-2 V, etc., the output of the eighth comparator the value 7-8 V. In contrast to this, in accordance with the invention three comparators are sufficient and each discrete measured value is represented by the total of all output signals of all comparators, namely by a measurement signal comprised of three bits and present in coded form.
As stated above, a method and a circuit arrangement for converting an analog measuring voltage into a digital measurement signal are the object of the invention. However, this need not be a linear conversion. It is possible to make any desired connection between the analog measuring voltage and the digital measurement signal; for example, the digital measurement signal to be realized can depend logarithmically or quadratically on the analog measuring voltage to be converted. Basically it is therefore possible with the use of the method according to the invention to convert the measurement voltage into an auxiliary voltage associated in the manner previously indicated with the measuring voltage and to first supply the auxiliary voltage to the inputs of the comparators.
Regarding the dependence of the digital measurement signal on the analog measuring voltage to be converted, a further teaching of the invention which, separately from the teaching of the invention described so far, is of distinct inventive importance, is characterized in that the measuring voltage is compared with a switch reference voltage and that at the time when the measuring voltage attains the switch reference voltage a switch signal is generated. Then, when the measuring voltage lies below the switch reference voltage, the difference between the switch reference voltage and the measuring voltage is preferably obtained as auxiliary voltage and when the measuring voltage lies above the switch reference voltage, the difference between the measuring voltage and the switch reference voltage is obtained. The circuit arrangement corresponding to this, which is also of independent inventive importance, is characterized in that a voltage converter is provided at the input side and in that the voltage converter converts the measuring voltage into an auxiliary voltage assigned to the measuring voltage, the voltage converter preferably having a threshold switch, and in that the threshold switch generates a switch signal at the time when the measuring voltage reaches the switch reference voltage, the voltage converter furthermore preferably having a differential amplifier and an inverter and, finally, the differential amplifier and the inverter preferably generating at the time when the measuring voltage lies below the switch reference voltage, the difference between the switch reference voltage and the measuring voltage as auxiliary voltage and generating at a time when the measuring voltage lies above the switch reference voltage, the difference between the measuring voltage and the switch reference voltage as auxiliary voltage.
In detail there are many possibilities to arrange and improve the teaching of the invention. On the one hand, reference is made to the claims dependent on claim 1. On the other hand, the drawings having as their content a preferred embodiment of a circuit arrangement in accordance with the invention, serve as a description.